A bit disconcerting but recently I had a massive drop in oil pressure. From a normal running PSI of around 40 it dropped to below 20 at 3000 rpm and whilst sat at traffic lights it dropped from a normal 20 to zero.


Zero psi on tick over


Less than 20 psi at 3000 rpm.

Now I checked by looking in the oil cap that I had oil at the top of the engine on tick over so I was not that concerned. I had no oil leaks so it had to be either the gauge, sender or something blocking the pressure relief valve.
Last week I bit the bullet and got under the car and removed the oil filter housing from the side of the engine. Not a difficult job other than access to the five ½ bolts. Once the bolts were out (you have to leave the bottom front bolt in situ as it fouls on the steering box) a screw driver to release the jubilee clip on the bypass hose and the housing slides out. On the bench the housing was checked, the pressure release valve was stripped and cleaned and there was nothing obviously wrong with it.


Oil filter housing with screw on filter modification.


Oil pressure relief valve.

The housing was refitted (not forgetting to insert the lower front bolt first before offering it up) and everything tightened. Checked the oil pressure and it was still showing no pressure.

OK next was the oil pressure sender. Not a cheap part as they are nearly £90 at SNG which is why I went for the pressure release valve first, but I bit the bullet and ordered a new one. It arrived today and although again it is difficult to get to, an 18mm spanner with one arm down the front of the carbs and the other down the back and I was able to release the old and fit the new. Started up the engine and Hey Presto, oil pressure back up to 25 psi on tick over and over 40 at 3000 rpm.

Naughty old Oil pressure sender telling me lies.



25 psi at tick over

Over 40 psi at 3000 rpm.

 

A job well done!

 

Those Oil pressure senders/sensors are notorious for failing. You did the right thing by checking oil flow to the cams. If it's OK then it's always that damn sensor unit. Barratts tell me that the new ones are far more reliable. We shall see.

 

I have just had a battle with an excessive reading on my MK2.
At first thought the oil pressure relief valve was the problem but it was OK.
I then fastened a mechanical gauge to the system and the oil pressure was quite normal.
It's that unreliable sender again.!!!
I am looking at alternative gauge systems.
My experience with MK1 and earlier cars like MK5 and MK7 is that the old Bowden tube direct reading gauges were much more reliable and accurate.

 

Bill ~ with all your experience have you ever seen an oil pressure relief valve fail to operate properly? I have not.

 

If the latest senders are good, as good as the originals from the 1960s, I'd replace the sender and stick with the electric system. Otherwise, it's swap to a Bourdon tube. As I've mentioned before the long capillary tube worries me a bit. The compromise might be to keep the electric gauge on the dash and have a Bourdon permanently installed on the side of the engine.

 

Never seen one fail but many years ago I had one leg of a split pin shear off and this lodged in the relief valve keeping it open so I had no oil pressure. This was severe but other things can get stuck in them keeping them open. An over zealots use of gasket paste can be a cause as this tends to peel off the inside of the joint and go into the oil flow.

 

Yes ~ that makes sense.

 

Glyn
I have seen a couple of cases where the oil pressure relief valve was worn and low pressure resulted. This was typically due to the face of the valve getting worn in slight asymmetry.
That in turn was due to wear in the relief valve shaft. A quick fix was to reface the valve piston in a lathe which generally resulted in a fix which was not perfect but did the job in restoring oil pressure.

I did run into an overpressure in a relief valve which was caused by a person or persons unknown packing the spring with washers in an attempt to increase oil pressure on a worn engine.
Obviously not a fix for the problem. That is why I checked the relief valve in the first place suspecting similar dastardly deeds.

Re my previous; I am sniffing around to try and find a compatible modern sender to match the original gauge.
At 90 English pounds, a new sender will end up costing well over A$200, probably closer to 250 with the exorbitant English postage rates.

I think I have previously mentioned a case where I had to shut an engine down in a twin engine Aerocommander not long after take-off due to falling oil pressure because the oil pressure relief valve was stuck partially open.

 

Three years ago I experienced a drop in oil pressure that turned out to be due to wear of the pressure relief valve. The flutes on the valve wore such that the sealing face did not sit evenly on the mating face.
I wrote up a memo and took some pictures in case anyone was interested.
They are attached
Bruce

Face uneven wear

Uneven wear


Wear on flute face

Wear on housing face

 

Even after I replaced my sender, the gauge would still drop to zero at highway speeds _ see this.

https://www.jaguarforums.com/forum/m...2/#post2576146

 

Does anyone know what the output of the sender is? I'm assuming it changes resistance with pressure, it would be interesting to know the specs and see if there is something else that is cheaper/more reliable out there.

 

JB ~ All I know is that it is a varying resistive sender vs a varying voltage sender. At the time of looking at this expensive piece of kit once the courier got it to SA I remember checking VDO, Quinton Hazell etc. and they were all calibrated for vehicles that run far higher oil pressure than the XK. e,g. Aston etc. at 100psi>.

EDIT: You could buy a VDO sender at the time for $10.

 

Jagboi, see my post no 11 in the link given by Jeff above. All you need to know is in the two attached, 'Gentleman's guides.'

 

i.e. they are varying resistive senders as I say above.

 

Thanks, those guides are quite comprehensive.

 

Quick up date.
The oil pressure sender that SNG sent me and was fitted is now playing up. Driving along happily with the gauge showing 40 psi then suddenly it goes all the way to the top of the gauge, 60 psi, where is stays for a couple of mins before dropping back to zero then back to normal at 40 psi. Could be the gauge but I contacted SNG who have sent out a new sender which should be here tomorrow. I have to send the old one back for testing but if this new one plays up at least I should know if it is the gauge or not. I am in the middle of refurbing a spare gauge so if I have further troubles I will swap the gauges over.

 

Full deflection on the gauge usually means a short to earth, so the sender could be failing internally.

 

Two in a row would seem unlikely unless the batch is bad. Could be wiring or gauge. I would be suspicious of gauge. Let's see how the next sensor goes. I thought your existing sensor was new? I thought you commented a while back on the Register but my brain is tired ~ Bedtime. These sensors don't have a great reputation but Barratts told me they were now a lot more reliable.

 

They are fairly simple devices and should behave consistently if not giving great accuracy. Apart from the gauge and the sender, are the cable and connectors all sound?